This invention relates to the field of Electrically Programmable Read-Only Memory (EPROM) devices. More specifically, it relates to shield structures which protect EPROMs from radiation.
Metal-Oxide-Semiconductors (MOS) Electrically Programmable Read Only Memories (EPROMs) have been utilized for the storage of information in prior art. U.S. Pat. No. 3,996,657 describes a typical cell for the above memories. These memory cells are susceptible to ultraviolet ("UV") radiation, and upon exposure to the radiation their contents are erased. These memory cells are used to construct arrays of memory cells as described in U.S. Pat. Nos. 3,728,695 and 3,744,036.
Redundant rows and columns have been utilized in prior art for replacing defective rows and columns in Read-Only Memories (ROMs) and Random-Access Memories (RAMs). Fusible silicon links are used to enable these redundant elements. (A process for making a PROM employing fusible silicon links is described in U.S. Pat. No. 3,792,319.) U.S. Pat. No. 4,250,570, for example, describes a memory employing redundant elements.
It is an object of the present invention to provide a shield to protect areas of an integrated circuit which is sensitive to radiation.
It is another object of the present invention to provide a shield that includes signal paths to access the above sensitive areas from all directions.
It is yet another object of the present invention to provide shielded memory cells that can be used in place of the above-mentioned fusible silicon links.